The demand for electronics device grade single crystal diamonds has been increasing steadily through the years due to its wide-range of scientific and industrial applications, beside gems. The remarkable intrinsic properties of electronic grade single crystal diamonds is one of the reasons why it is a preferred material for industrial and scientific applications, as well as gems.
Diamond deposition by CVD process on various solid substrates have been extensively described in various patent documents and also extensively investigated by researchers and published in scientific journals and other technical literatures. The process of diamond growth by CVD process involves the deposition of carbon atoms that originate from the dissociation of a carbon-containing gas precursor (i.e. CxHy (x=1 to 4)) on a solid substrate under the reaction of a mixture of several gases (H2, Ar, O2, Nb2, COx, CFx etc.). Polycrystalline or single crystal CVD diamonds can be produced and their crystalline quality strongly depends not only on the process chemistry of the gases used, but also on the nature and condition of the solid substrate as well. It is a well-established method to nucleate diamond internally in the conventional growth of microcrystalline diamond films to use a hydrocarbon-rich mixture of hydrocarbon-hydrogen precursor gases.
Several patent documents and scientific literatures disclose various methods of producing large poly-crystalline diamond films for radiation wave detection. The disadvantages of these large poly-crystalline diamond films is that the firms are not only limited in thickness but also limited in charge collection distance due to the presence of grain boundaries that drastically affect their electronic properties.
European patent publication No. EP19830380A2 discloses the method of producing diamonds suitable for electronic applications by CVD process. However, the electronics properties of these diamonds are believed to be affected by the presence of minute impurities (>1 ppm) and lattice defects which will reduces their charge collection efficiency/distance. Production of full collection distance at lower bias field (<0.2V/μm) detectors based on single crystal diamond with extremely high reproducibility through sufficient control of the growth process and tight selection of solid substrate by CVD process has not been disclosed.
U.S. Pat. No. 7,887,628 discloses a layer of single crystal CVD diamond having a thickness of greater than 2 mm, wherein the layer has a level of any single impurity of not greater than 1 ppm and a total impurity content of not greater than 5 ppm whereby the impurity excludes hydrogen in isotopic forms and in electron paramagnetic resonance (EPR), a single substitutional nitrogen centre [N—C]0 at a concentration <100 ppb.
US Patent Application Publication 2013/0202518 discloses a single crystal CVD diamond having a level of any single impurity of not greater than 5 ppm and a total impurity content of not greater than 10 ppm wherein impurity excludes hydrogen in isotopic forms, and in electron paramagnetic resonance (EPR), a single substitutional nitrogen centre [N—C]0<40 ppb.
It is an object of the present invention to provide a method of utilising microwave plasma chemical vapour deposition (MPCVD) process to produce electronic device grade single crystal diamonds having a size up to 10×10×2 mm3 and also with a charge collection efficiency (CCE) of 100% when the bias field is at least 0.2 V/μm.
The reason of growing thick electronic device grade single crystal diamond is to prevent the formation of crystal defects such as thread dislocations, crystal plane twining, “petal-shape” defects and step-growth related dislocations. Generally, these crystal defects grow and propagate during growth and eventually results in highly stressed MPCVD diamonds. These stresses are known to degrade the charge carrier mobilities and lifetimes of diamond based detectors. The method described herein includes the step of pre-growth conditioning on the diamond substrate so as to suppress the crystal defects from growing and preparing the substrates that are substantially free of crystal defects and impurities.
Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.